The present invention is generally directed to a modular override valve for a fuel system for an engine, and more particularly to a battle override valve for operating an engine during an electrical or main fuel control system failure.
It is desirable in the background art of fuel systems to provide a manual bypass or override control function in order to provide backup or supplementary control of engine fuel systems during or subsequent to electronic or system failures, particularly in fuel systems for military vehicles.
U.S. Pat. No. 4,893,599 to Melnik et al., the entirety of which is hereby incorporated by reference, describes a manual bypass mechanism for an electronic fuel injection device on a military vehicle such as a tank. The mechanism described in the Melnik et al. patent is designed for use in an electronically controlled fuel system employing an electronic fuel unit (ECU) for a tank. As described by Melnik et al., the ECU is programmed to initiate several protective modes and reduces fuel flow from the HMU (Hydromechanical Unit) if certain performance irregularities occur in the engine, transmission, or other propulsion system component in order to prevent engine damage.
In one of the protective modes, referred to as xe2x80x9cprotective mode IIIxe2x80x9d, the flow rate of fuel to the engine is reduced to about 120 lbs./hour, so the engine generates only about 72 hp, or 5 percent of its capacity. The tank must move very slowly, e.g., at 1 mph, to a site where the propulsion system""s problem can be analyzed. In a battle or emergency scenario, it may be necessary to drive the tank faster than protective mode III permits. Further, it is possible that battle damage could cut off electrical power to the ECU and thereby adversely limit fuel flow to the engine.
The mechanism described by Melnik includes a completely mechanical fuel bypass device which routes additional fuel to the engine during protective mode III or during failure of the ECU. The device was a modular, add-on unit that can be installed on existing tanks without disassembly of the hydromechanical units and which can be used without modifying the logic of the ECUs.
However, the present inventors have determined that systems of the background art, including that described in the Melnik et al. patent, suffer from several shortcomings. Specifically, the Melnik device requires a screw-type metering valve/metering shaft for controlling fuel flow between a zero-flow position to a fully open position. In addition, the systems of the background art fail to include adequate consideration for protecting against engine overspeed and high temperatures when fuel control is shifted to the manual bypass device.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
The present invention, in part, is a recognition by the present inventors that a rate limiting function can be advantageously employed in a battle override valve for a fuel system of an engine.
The present invention, in part, is a recognition by the present inventors that a manually operated bypass fuel control valve incorporating fuel metering and fuel flow rate limiting functions will assist in avoiding excessive engine overspeeding and/or overheating conditions during manual operation, e.g. bypass fuel control.
The present invention, in part, is recognition by the present inventors that a minimum slew rate provided by a bypass fuel control valve will provide a smooth transition between manual (bypass) and automatic fuel system control while simultaneously preventing undesirable engine shutoff or stalling.
One or more of the foregoing aspects of the present invention is accomplished, in part, by a bypass fuel control device for an engine fuel system comprising a metering valve having a rate limiting device, wherein the rate limiting device provides for control of a slew rate during an operation of the battle override valve; a transfer valve having a manual fuel control operating position and a normal fuel control operating position, wherein the manual fuel control operating position permits a flow of fuel between the metering valve and the transfer valve; and a control device controlling a movement of the transfer valve between the normal fuel control operating position and the manual fuel control operating position.
One or more of the foregoing aspects of the present invention is also accomplished, in part, by a bypass fuel control device for a manual operation of an engine fuel system comprising a metering valve having a rate limiting device, wherein said rate limiting device provides for control of a fuel delivery rate during an operation of the battle override valve; a spool and a sleeve valve device for controlling a metered fuel flow of the metering valve; a low pressure bleed assembly within said metering valve; and a control spring, wherein said low pressure bleed assembly and said control spring provide said rate limiting effect for controlling said fuel delivery rate.
One or more of the foregoing aspects of the present invention is also accomplished, in part, by a fuel control system for an engine, the fuel control system comprising a fuel supply; a fuel pump providing a supply of fuel to the engine; an electronic flow control system providing an automatic operation of the fuel system during a normal engine operation; a fuel output to the engine; and a bypass fuel control device providing a manual operation of the fuel system during a bypass engine operation, the bypass fuel control device including a metering valve having a rate limiting device, wherein the rate limiting device provides for control of a slew rate during an operation of the bypass fuel control device, a transfer valve controlling a supply and a return of fuel respectively to and from the metering valve, and a control device controlling a position of the transfer valve between a normal operating position and a bypass operating position.
One or more of the foregoing aspects of the present invention is accomplished, in part, by a method of controlling a bypass fuel supply for an engine fuel control system having the aforementioned bypass fuel control device, the method comprising the steps of controlling the bypass fuel supply flow with the metering valve, wherein an increase in the bypass fuel supply flow is delayed by the rate limiting effect of the metering valve; and controlling the fuel supply and return of respectively to and from the metering valve with the transfer valve.